var imgs = new Array( 'logo-01.jpg', 'logo-02.jpg', 'logo-03.jpg');
var pos = 0;

function chImg()
{
var i = document.getElementById( 'imgField' );

i.src = './img/' + imgs[ pos++ ];

if( pos >= 3 )
{
pos = 0;
}

window.setTimeout( 'chImg()', 5000 );
}